.TH std::flat_map::emplace 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::flat_map::emplace \- std::flat_map::emplace

.SH Synopsis
   template< class... Args >                             (since C++23)
   std::pair<iterator, bool> emplace( Args&&... args );

   Inserts a new element into the container constructed in-place with the given args,
   if there is no element with the key in the container.

   Initializes an object t of type std::pair<key_type, mapped_type> with
   std::forward<Args>(args)...; if the map already contains an element whose key is
   equivalent to t.first, *this is unchanged. Otherwise, equivalent to:

 auto key_it = ranges::upper_bound(c.keys, t.first, compare);
 auto value_it = c.values.begin() + std::distance(c.keys.begin(), key_it);
 c.keys.insert(key_it, std::move(t.first));
 c.values.insert(value_it, std::move(t.second));

   This overload participates in overload resolution only if
   std::is_constructible_v<std::pair<key_type, mapped_type>, Args...> is true.

   Careful use of emplace allows the new element to be constructed while avoiding
   unnecessary copy or move operations.

    Information on iterator invalidation is copied from here

.SH Parameters

   args - arguments to forward to the constructor of the element

.SH Return value

   A pair consisting of an iterator to the inserted element (or to the element that
   prevented the insertion) and a bool value set to true if and only if the insertion
   took place.

.SH Exceptions

   If an exception is thrown for any reason, this function has no effect (strong
   exception safety guarantee).

.SH Complexity

   If insertion occurs, linear in the size of the container, otherwise logarithmic in
   the size of the container

.SH Example


// Run this code

 #include <iostream>
 #include <string>
 #include <utility>
 #include <flat_map>

 int main()
 {
     std::flat_map<std::string, std::string> m;

     // uses pair's move constructor
     m.emplace(std::make_pair(std::string("a"), std::string("a")));

     // uses pair's converting move constructor
     m.emplace(std::make_pair("b", "abcd"));

     // uses pair's template constructor
     m.emplace("d", "ddd");

     // emplace with duplicate key has no effect
     m.emplace("d", "DDD");

     // uses pair's piecewise constructor
     m.emplace(std::piecewise_construct,
               std::forward_as_tuple("c"),
               std::forward_as_tuple(10, 'c'));
     // an alternative is: m.try_emplace("c", 10, 'c');

     for (const auto& p : m)
         std::cout << p.first << " => " << p.second << '\\n';
 }

.SH Output:

 a => a
 b => abcd
 c => cccccccccc
 d => ddd

.SH See also

   emplace_hint constructs elements in-place using a hint
                \fI(public member function)\fP
                inserts in-place if the key does not exist, does nothing if the key
   try_emplace  exists
                \fI(public member function)\fP
   insert       inserts elements
                \fI(public member function)\fP
